The present invention relates to a flexible fluid containment vessel (sometimes hereinafter referred to as xe2x80x9cFFCVxe2x80x9d) for transporting and containing a large volume of fluid, particularly fluid having a density less than that of salt water, more particularly, fresh water, and the method of making the same.
The use of flexible containers for the containment and transportation of cargo, particularly fluid or liquid cargo, is well known. It is well known to use containers to transport fluids in water, particularly, salt water.
If the cargo is fluid or a fluidized solid that has a density less than salt water, there is no need to use rigid bulk barges, tankers or containment vessels. Rather, flexible containment vessels may be used and towed or pushed from one location to another. Such flexible vessels have obvious advantages over rigid vessels. Moreover, flexible vessels, if constructed appropriately, allow themselves to be rolled up or folded after the cargo has been removed and stored for a return trip.
Throughout the world there are many areas which are in critical need of fresh water. Fresh water is such a commodity that harvesting of the ice cap and icebergs is rapidly emerging as a large business. However, wherever the fresh water is obtained, economical transportation thereof to the intended destination is a concern.
For example, currently an icecap harvester intends to use tankers having 150,000 ton capacity to transport fresh water. Obviously, this involves, not only the cost in using such a transport vehicle, but the added expense of its return trip, unloaded, to pick up fresh cargo. Flexible container vessels, when emptied can be collapsed and stored on, for example, the tugboat that pulled it to the unloading point, reducing the expense in this regard.
Even with such an advantage, economy dictates that the volume being transported in the flexible container vessel be sufficient to overcome the expense of transportation. Accordingly, larger and larger flexible containers are being developed. However, technical problems with regard to such containers persist even though developments over the years have occurred. In this regard, improvements in flexible containment vessels or barges have been taught in U.S. Pat. Nos. 2,997,973; 2,998,973; 3,001,501; 3,056,373; and 3,167,103. The intended uses for flexible containment vessels is usually for transporting or storing liquids or fluidisable solids which have a specific gravity less than that of salt water.
The density of salt water as compared to the density of the liquid or fluidisable solids reflects the fact that the cargo provides buoyancy for the flexible transport bag when a partially or completely filled bag is placed and towed in salt water. This buoyancy of the cargo provides flotation for the container and facilitates the shipment of the cargo from one seaport to another.
In U.S. Pat. No. 2,997,973, there is disclosed a vessel comprising a closed tube of flexible material, such as a natural or synthetic rubber impregnated fabric, which has a streamlined nose adapted to be connected to towing means, and one or more pipes communicating with the interior of the vessel such as to permit filling and emptying of the vessel. The buoyancy is supplied by the liquid contents of the vessel and its shape depends on the degree to which it is filled. This patent goes on to suggest that the flexible transport bag can be made from a single fabric woven as a tube. It does not teach, however, how this would be accomplished with a tube of such magnitude. Apparently, such a structure would deal with the problem of seams. Seams are commonly found in commercial flexible transport bags, since the bags are typically made in a patch work manner with stitching or other means of connecting the patches of water proof material together. See e.g. U.S. Pat. No. 3,779,196. Seams are, however, known to be a source of bag failure when the bag is repeatedly subjected to high loads. Seam failure can obviously be avoided in a seamless structure. However, since a seamed structure is an alternative to a simple woven fabric and would have different advantages thereto, particularly in the fabrication thereof, it would be desirable if one could create a seamed tube that was not prone to failure at the seams.
In this regard, U.S. Pat. No. 5,360,656 entitled xe2x80x9cPress Felt and Method of Manufacturexe2x80x9d, which issued Nov. 1, 1994 and is commonly assigned, the disclosure of which is incorporated by reference herein, discloses a base fabric of a press felt that is fabricated from spirally wound fabric strips. The fabric strip of yarn material, preferably being a flat-woven fabric strip, has longitudinal threads which in the final base fabric make an angle in what would be the machine direction of a press felt.
During the manufacture of the base fabric, the fabric strip of yarn material is wound or placed spirally, preferably over at least two rolls having parallel axes. Thus, the length of fabric will be determined by the length of each spiral turn of the fabric strip of yarn material and its width determined by the number of spiral turns.
The number of spiral turns over the total width of the base fabric may vary. The adjoining portions of the longitudinal edges of the spirally-wound fabric strip are so arranged that the joints or transitions between the spiral turns can be joined in a number of ways.
An edge joint can be achieved, e.g. by sewing, melting, and welding (for instance, ultrasonic welding as set forth in U.S. Pat. No. 5,713,399 entitled xe2x80x9cUltrasonic Seaming of Abutting Strips for Paper Machine Clothingxe2x80x9d which issued Feb. 3, 1998 and is commonly assigned, the disclosure of which is incorporated herein by reference) of non-woven material or of non-woven material with melting fibers. The edge joint can also be obtained by providing the fabric strip of yarn material along its two longitudinal edges with seam loops of known type, which can be joined by means of one or more seam threads. Such seam loops may for instance be formed directly of the weft threads, if the fabric strip is flat-woven.
While that patent relates to creating a base fabric for a press felt such technology may have application in creating a sufficiently strong tubular structure for a transport container. Moreover, with the intended use being a transport container, rather than a press fabric where a smooth transition between fabric strips is desired, this is not a particular concern and different joining methods (overlapping and sewing, bonding, stapling, etc.) are possible. Other types of joining may be apparent to one skilled in the art.
It should be noted that U.S. Pat. No. 5,902,070 entitled xe2x80x9cGeotextile Container and Method of Producing Samexe2x80x9d issued May 11, 1999 and assigned to Bradley Industrial Textiles, Inc. does disclose a helically formed container. Such a container is, however, intended to contain fill and to be stationary rather than a transport container.
Returning to the particular application to which the present invention is directed, other problems face the use of large transport containers. In this regard, when partially or completely filled flexible barges or transport containers are towed through salt water, problems as to instability are known to occur. This instability is described as a flexural oscillation of the container and is directly related to the flexibility of the partially or completely filled transport container. This flexural oscillation is also known as snaking. Long flexible containers having tapered ends and a relatively constant circumference over most of their length are known for problems with snaking. Snaking is described in U.S. Pat. No. 3,056,373, observing that flexible barges having tapered ends build up to damaging oscillations capable of seriously rupturing or, in extreme cases, destroying the barge, when towed at a speed above a certain critical speed. Oscillations of this nature were thought to be set up by forces acting laterally on the barge towards its stern. A solution suggested was to provide a device for creating breakaway in the flow lines of the water passing along the surface of the barge and causing turbulence in the water around the stern. It is said that such turbulence would remove or decrease the forces causing snaking, because snaking depends on a smooth flow of water to cause sideways movement of the barge.
Other solutions have been proposed for snaking by, for example, U.S. Pat. Nos. 2,998,973; 3,001,501; and 3,056,373. These solutions include drogues, keels and deflector rings, among others.
Another solution for snaking is to construct the container with a shape that provides for stability when towing. A company known as Nordic Water Supply located in Norway has utilized this solution. Flexible transport containers utilized by this company have a shape that can be described as an elongated hexagon. This elongated hexagon shape has been shown to provide for satisfactory stable towing when transporting fresh water on the open sea. However, such containers have size limitations due to the magnitude of the forces placed thereon. In this regard, the relationship of towing force, towing speed and fuel consumption for a container of given shape and size comes into play. The operator of a tugboat pulling a flexible transport container desires to tow the container at a speed that minimizes the cost to transport the cargo. While high towing speeds are attractive in terms of minimizing the towing time, high towing speeds result in high towing forces and high fuel consumption. High towing forces require that the material used in the construction of the container be increased in strength to handle the high loads. Increasing the strength typically is addressed by using thicker container material. This, however, results in an increase in the container weight and a decrease in the flexibility of the material. This, in turn, results in an increase in the difficulty in handling the flexible transport container, as the container is less flexible for winding and heavier to carry.
Moreover, fuel consumption rises rapidly with increased towing speed. For a particular container, there is a combination of towing speed and fuel consumption that leads to a minimum cost for transportation of the cargo. Moreover, high towing speeds can also exacerbate problems with snaking.
In the situation of the elongated hexagon shaped flexible transport containers used in the transport of fresh water in the open sea, it has been found, for a container having a capacity of 20,000 cubic meters, to have an acceptable combination of towing force (about 8 to 9 metric tons), towing speed (about 4.5 knots) and fuel consumption. Elongated hexagon shaped containers having a capacity of 30,000 cubic meters are operated at a lower towing speed, higher towing force and higher fuel consumption than a 20,000 cubic meter cylindrical container. This is primarily due to the fact that the width and depth of the larger elongated hexagon must displace more salt water when pulled through open sea. Further increases in container capacity are desirable in order to achieve an economy of scale for the transport operation. However, further increases in the capacity of elongated hexagon shaped containers will result in lower towing speeds and increased fuel consumption.
The aforenoted concerning snaking, container capacity, towing force, towing speed and fuel consumption defines a need for an improved flexible transport container design. There exists a need for an improved design that achieves a combination of stable towing (no snaking), high FFCV capacity, high towing speed, low towing force and low fuel consumption relative to existing designs.
In addition, to increase the volume of cargo being towed, it has been suggested to tow a number of flexible containers together. Such arrangements can be found in U.S. Pat. Nos. 5,657,714; 5,355,819; and 3,018,748 where a plurality of containers are towed in line one after another. So as to increase stability of the containers, EPO 832 032 B1 discloses towing multiple containers in a pattern side by side.
However, in towing flexible containers side by side, lateral forces caused by ocean wave motion creates instability which results in one container pushing into the other and rolling end over end. Such movements have a damaging effect on the containers and also effect the speed of travel.
Furthermore, while as aforenoted, a seamless flexible container is desirable and has been mentioned in the prior art, the means for manufacturing such a structure has its difficulties. Heretofore, as noted, large flexible containers were typically made in smaller sections which were sewn or bonded together. These sections had to be water impermeable. Typically such sections, if not made of an impermeable material, could readily be provided with such a coating prior to being installed. The coating could be applied by conventional means such as spraying or dip coating.
Accordingly, there exists a need for a FFCV for transporting large volumes of fluid which overcomes the aforenoted problems attendant to such a structure and the environment in which it is to operate.
It is therefore a principal object of the invention to provide for a relatively large spirally formed fabric FFCV for the transportation of cargo, including, particularly, fresh water, having a density less than that of salt water.
It is a further object of the invention to provide for such an FFCV which has means of inhibiting the undesired snaking thereof during towing.
It is a further object of the invention to provide means for allowing the transportation of a plurality of such FFCVs.
A further object of the invention is to provide for a means for reinforcing of such an FFCV so as to effectively distribute the load thereon and inhibit rupture.
A yet further object is to provide for a means of rendering the tube used in the FFCV impermeable.
These and other objects and advantages will be realized by the present invention. In this regard the present invention envisions the use of a spirally formed tube to create the FFCV, having a length of 300xe2x80x2 or more and a diameter of 40xe2x80x2 or more. Such a large structure can be fabricated in a manner set forth in U.S. Pat. No. 5,360,656 and on machines that make papermaker""s clothing such as those owned and operated by the assignee hereof. The ends of the tube, sometimes referred to as the nose and tail, or bow and stern, are sealed by any number of means, including being folded over and bonded and/or stitched with an appropriate tow bar attached at the nose. Examples of end portions in the prior art can be found in U.S. Pat. Nos. 2,997,973; 3,018,748; 3,056,373; 3,067,712; and 3,150,627. An opening or openings are provided for filling and emptying the cargo such as those disclosed in U.S. Pat. Nos. 3,067,712 and 3,224,403.
In addition, through the use of the spiral strip method, the bow or stern or both can be tapered in, for example, a cone shape or other shape suitable for the purpose.
In order to reduce the snaking effect on such a long structure, a plurality of longitudinal stiffening beams are provided along its length. These stiffening beams are intended to be pressurized with air or other medium. The beams may be formed as part of the tube or woven separately and maintained in sleeves which may be part of the FFCV. They may also be braided in a manner as set forth in U.S. Pat. Nos. 5,421,128 and 5,735,083 or in an article entitled xe2x80x9c3-D Braided Composites-Design and Applicationsxe2x80x9d by D. Brookstein, 6th European Conference on Composite Materials, September 1995. They can also be knit or laid up. The tube is preferably the spiral method heretofore described. Attaching or fixing such beams by sewing or other means to the tube is possible, however, unitized construction is preferred due to the ease of manufacturing and its greater strength.
Stiffening or reinforcement beams of similar construction as noted above may also be provided at spaced distances about the circumference of the tube.
The beams also provide buoyancy to the FFCV as the cargo is unloaded to keep it afloat, since the empty FFCV would normally be heavier than salt water. Valves may be provided which allow pressurization and depressurization as the FFCV is wound up for storage.
In the situation where more than one FFCV is being towed, it is envisioned that one way is that they be towed side by side. To increase stability and avoid xe2x80x9croll overxe2x80x9d a plurality of beam separators, preferably containing pressurized air or other medium, would be used to couple adjacent FFCVs together along their length. The beam separators can be affixed to the side walls of the FFCV by way of pin seam connectors or any other means suitable for purpose.
Another way would be by constructing a series of FFCVs interconnected by a flat spiral formed portion.
The present invention also discloses methods rendering the tube impervious. The fabric strip can be coated on the inside, outside, or both with an impervious material. When formed into the tube, the seams may be further coated.